The present invention relates generally to the successive indexing of products to an operating station and, in particular, to the indexing of products from a moving conveyor system to a stationary position for operations thereon performed by robots and then returning the products to the moving conveyor system.
Most industrial robots are designed to perform operations on products under fabrication only when the products are stationarily positioned at the robot station, whereas most manual production operations are performed while the products are continuously moving. The integration of robotic operations with manual operations in the same manufacturing or assembly facility has, therefore, created the need for conveyor systems capable of both continuous and intermittent movement.
The integration of robots with moving conveyors requires that the products be disengaged from a continuously moving constant speed conveyor, then rapidly indexed to a stationary position at a robot, and then, after the robotic operation is complete, the products must be reinserted into the identical sequence on the conveyor. The disengagement, indexing, robotic operation and return of the product must all be accomplished within the time limits established by the speed of the moving conveyor (i.e., in a conveyor system which operates at 60 product assemblies per hour, a total cycle time of one minute is available).
The design objective of such an integrated conveyor system is to provide a means of indexing products from the moving conveyor to the stationary position at a robot station in a smooth and safely controlled manner while allowing the maximum amount of the total time cycle for the operation of the robot. Time, therefore, is a critical factor. Furthermore, the system should have the ability to isolate the robot from the moving conveyor such that minor delays in robot functions do not cause the moving conveyor to stop; the ability to accomodate singular or multiple robot stations; the ability to accomodate additional stations in the future; and should require a minimum of factory floor space for installation of the system.
Prior methods of transferring products from a moving conveyor to a stationary position have consisted of separate chain conveyors which index and stop at the robots, or a system known as "Cartrak" which utilizes specially designed pallets which index by the interaction of a mechanism on each pallet with a continuously rotating drive tube. The prior art indexing chain conveyor requires that all products be indexed simultaneously, thereby requiring excessively oversized drive power units and also directly linking the robot time cycle to the continuously moving conveyor timing. Thus, if the robot malfunctions the conveyor immediately stops, which is extremely costly in manufacturing and assembly facilities. Indexing chain conveyors also typically require large pits in the plant floor to connect the chain in a loop and to mount the drive machinery.
The Cartrak system requires separate automatic or manual handling apparatus to transfer the products from the continuously moving conveyor to the separate Cartrak pallets and back onto the moving conveyor, plus an additional length of the Cartrak system is required to return empty pallets to the system start point, thus Cartrak requires excessive amounts of floor space and is costly. Therefore, these prior methods of transferring products for robotic operations have proven to be complicated and expensive.
It is, therefore, an important object of this invention to provide a positive means of rapidly indexing products for stationary robotic or other automated operations from a moving conveyor and then returning the products to the moving conveyor, without the complexity and expense characteristic of the prior systems discussed above.
Another important object of this invention is to provide an indexing conveyor that employs a shuttle characterized by positive acceleration, deceleration, and positioning with high speed indexing.
Still another important object of this invention is to provide an indexing conveyor having low energy usage and low horsepower requirements due to the mechanical advantages realized through utilization of a helically threaded drive shaft.
Yet another important object of this invention is to provide an indexing conveyor system which allows robots or other automated operations to be easily integrated with traditional assembly line operations both in new and existing facilities, and to provide such a system that is easily expanded or relocated for future use.
Furthermore, another important object of this invention is to provide an indexing conveyor which requires no pitwork or costly product transfers to separate pallets, and minimizes the plant floor space required to accomplish indexing.
Finally, another important object of this invention is to provide an indexing conveyor which operates independently of the main moving conveyor production lines, thereby reducing costly plant downtime.
Accordingly, the present invention is directed to an efficient and economical means of indexing products from a continuously moving conveyor to a stationary position for robotic operations or other operations requiring a stationary product, and then returning them to the moving conveyor if necessary.
For example, in an automotive assembly plant car bodies are typically conveyed on four-wheeled dollies which are towed along a floor track by a continuously moving chain conveyor. The present invention would index a car body placed on the four-wheeled dolly to the robot station and present both as a unit in a stationary position so the operation by the robot can be performed.
Briefly, the present invention comprises a movable shuttle carriage which receives the dolly or other product carrier and is propelled along the axis of a main drive shaft through the engagement of followers, located beneath the shuttle carriage, within a helical recess or thread in the circumference of the drive shaft. The controlled acceleration, deceleration, and positioning of the shuttle carriage and thereby the dolly are accomplished either by varying the rotational speed of a uniformly threaded drive shaft through the use of a variable speed motor, or by utilizing a variably threaded drive shaft driven by a constant speed motor. As the dolly bearing an automobile body product, for example, approaches the shuttle carriage by conveyance on the continuously moving chain conveyor, the chain conveyor disengages from the dolly at the pickup point of the shuttle. A pusher dog mounted on the shuttle carriage then engages the dolly to accelerate the coupled dolly and carriage upon rotation of the drive shaft. The dolly with product may be accelerated to a linear speed in excess of 200 feet per minute; then as the product approaches the robot station the shuttle carriage is decelerated until the dolly with product thereon stops at the robot station.
While the robot is performing its production operation, the shuttle carriage returns to its home position, the pickup point, to await the next dolly with an automobile body thereon. Meanwhile a subsequent, independent indexer unit placed in line with the operating station indexer unit engages the dolly and, upon completion of the robot operation, transfers it from the operating station, such as to a subsequent station or to a position for re-engagement with the moving chain conveyor.
In many applications two or more indexer units or sections in tandem will precede the robot operating station indexer unit to provide accumulation of the dollies. Additional indexing sections may also be included to provide accumulation as desired at other stages of the indexing conveyor system. In other applications, however, particularly those not associated with assembly lines, a single indexing unit of the present invention may meet the requirements of a given application.